Chemical manufacturers, energy supply companies, and other industries commonly store large quantities of liquid fluids in tanks, vessels or other receptacles. In many instances, these fluids are environmentally-contaminating, explosive, or otherwise dangerous. For example, certain substances, such as nitric acid, chloride, or ammonia, may environmentally contaminate or otherwise injure surrounding areas. Additionally or alternatively, certain volatile substances, such as gasoline, acetone, alcohols or chlorobenzene, may produce vapors which invite the danger of an explosion.
To supply the demands of the relevant industry, the fluids contained in these receptacles are usually pumped into a service pipe to convey the fluid to a desired location. A vertical turbine pump is usually the preferred, and sometimes also the only feasible, piece of equipment for this purpose. This preference is based on the fact that the storage receptacles are often buried in the ground or situated in other locations which cause the use of horizontal pumps to be impracticable if not impossible. Additionally, pump flow capacity requirements from 50 gpm to 200 gpm, and head requirements to 600 feet, make a vertical turbine pump the only logical and economical choice.
A vertical turbine pump typically comprises a housings a drive assembly attached to the housing, an impeller assembly located within the housing, and a vertical shaft assembly. "Housing" in this context corresponds to the collection of structural components of the pump, other than the drive assembly, the impeller assembly and the shaft assembly. These structural components would commonly include a drive-support portion which supports the drive assembly, a discharge portion which includes a tank-mounting section and which includes the discharge outlet of the pump, and a column portion which includes a diffuser-bowl section and which includes the suction inlet of the pump. Regarding the impeller assembly, it will usually comprise a set (or "stages") of impeller blades.
"Vertical shaft assembly" in this context corresponds to the collection of shaft-like components which transfer power from the drive assembly to the impeller assembly to produce the required hydraulic conditions. In a typical vertical turbine pump, these "shaft assembly" components will include a top or drive-interfacing section which is operatively coupled to (and sometimes actually considered part of) the drive assembly, a transfer section coupled to the top section via a keyed shaft coupling, and a bottom or impeller-rotating section on which the impeller assembly is mounted. Because the drive assembly is located outside of the housing and the impeller assembly is located within the housing, the pump shaft assembly passes through the housing at a point which may be called the "shaft-opening", and a sealing mechanism is required in this area to prevent leakage from the housing.
When the drive assembly rotates the vertical shaft assembly, and thus the impeller assembly, the working fluid is drawn through the suction inlet of the pump and discharged at a higher pressure at the pump discharge outlet. More particularly, fluid is drawn into a central region of each impeller blade and is discharged at a higher pressure and a higher temperature at the blade's periphery. The major portion of the velocity energy is then converted into pressure energy by an impeller-interfacing section of the housing which surrounds the impeller periphery. This impeller-interfacing section of the housing usually comprises a set of complimentary stationary diffusion blades.
A pump may incorporate a mechanical drive assembly having a drive rotor which is mechanically coupled to the pump shaft assembly and which therefore mechanically conveys rotational motion thereto. Such drive assemblies have conventionally been successfully used on both horizontal and vertical pumps. However, the shaft-opening on the pump housing has traditionally been a prime culprit of liquid and/or vapor leakage in mechanical drive pumps. Although mechanical drive vertical turbine pumps have been developed which minimize liquid leakage to an acceptable level, these designs do not eliminate vapor leakage. Consequently, a vertical turbine pump incorporating such a mechanical drive assembly can often not be used in applications where environmental contamination, explosion or other dangerous consequences are a concern.
Certain pumps may alternatively incorporate a magnetic drive assembly. In a magnetic drive assembly, the pump shaft assembly is not mechanically coupled to the drive rotor, and in fact, it does not actually physically contact the drive rotor during operation. Instead, the rotational motion of the drive assembly is "magnetically conveyed" to the pump shaft assembly. The term "magnetically conveyed" in this context corresponds to a conveyance of motion between two components in which essentially the only conveying force is magnetic in nature.
In a typical magnetic drive pump, a first magnetic member, which is annular in shape, is fixedly attached to the rotor; while a second magnetic member is attached to the drive-interfacing end of the shaft assembly. The drive-interfacing end of the shaft assembly is situated in a drive-interfacing position within the rotor, or within the opening defined by the first annular member. The magnetic members are specifically designed so that magnetic forces therebetween are such that when the shaft assembly is placed in a drive-interfacing position, rotational motion of the rotor will magnetically convey rotational motion to the pump shaft assembly.
Chempump Inc. (a subsidiary of the same parent company as the assignee of this application) and other manufacturers have successfully developed a magnetic drive assembly which eliminates liquid and vapor leakage usually associated with the shaft assembly-opening in the pump housing. However, unfortunately, such magnetic drive assemblies cannot be incorporated into vertical turbine pumps due to "down-thrust" complications. "Down-thrust" is the summation of impeller and gravity forces acting in the axial, and downward, direction, and such forces are quite significant, in high-head vertical pumps. Although down-thrust complications may be easily remedied in a mechanical drive pump by the design of the mechanical rotor-shaft connection, such a simple cure is not available for magnetic drive pumps because the pump shaft assembly is not mechanically connected to the drive rotor.
Applicants therefore believe that a need remains for a vertical turbine pump which incorporates a magnetic drive assembly whereby environmentally-contaminating, explosive, and otherwise dangerous fluids may be safely pumped.